1. Field of the Invention
The present invention relates to a system, in which a plurality of electronic apparatuses are connected by a bus, such as the IEEE1394 serial bus, capable of transmitting isochronous packets and asynchronous packets, which perform communications among those electronic apparatuses. More particularly, the present invention relates to technology that efficiently transmits data having a small amount of data, such as still image data, text data, icon bit map data, and the like.
2. Description of the Related Art
A system has been conceived in which electronic apparatuses (hereinafter referred to as apparatuses), such as a digital video cassette recorder, a television receiver, or a personal computer, are connected by the IEEE1394 serial bus (hereinafter referred to as a 1394 bus), and information signals, such as video data or audio data, and control signals, such as an operation control command or a connection control command of the apparatus, are communicated among these apparatuses.
In a system in which a plurality of apparatuses are connected by a 1394 bus, transmission of packets is performed by time-division multiplexing at every predetermined communication cycle (for example, 125 xcexcsec). This packet transmission is started when an apparatus called a cycle master sends a cycle start packet indicating the start of a communication cycle onto the 1394 bus. For communications in one communication cycle, there are two types of communications of isochronous (hereinafter referred to as Iso) communication in which information signals, such as video data or audio data, are transmitted in real time and asynchronous (hereinafter referred to as Async) communication in which a control signal, such as an operation control command or a connection control command of the apparatus, is transmitted at non-fixed intervals as required. The Iso packet is transmitted earlier than the Async packet. Attaching a channel number to each of the Iso packets makes it possible to distinguish among a plurality of Iso data. After transmission of all the Iso packets to be transmitted is completed, the period to the next cycle start packet is used for the transmission of Async packets.
In a system such as that described above, in which a plurality of apparatuses are connected by the 1394 bus, it has been proposed that information signals be handled by an audio-video/control (AV/C) descriptor model (Japanese Patent Application No. 9-96874 (corresponding U.S. Pat. No. 054,183 filed on Apr. 2, 1998), Japanese Patent Application No. 9-177917). More specifically, for example, contents, such as a service list of a digital tuner or a track list of a disk player, which can be selected from a data source, are held in the form of an object list in a memory within an apparatus by using an object having the structure shown in FIG. 13. When a desired object is specified from the object list, the data stream of the object is output from the apparatus by using the Iso packets.
Transmission of still data, such as still image data, text data, or icon bit map data, among apparatuses connected by the 1394 bus, has been conceived. Of course, it is possible to hold the list of these data inside the apparatus as the above-described object list and to transmit the selected data by using Iso packets. However, unlike data, such as audio data or video data, that requires a synchronization signal, these data have a small amount of data and no merits of transmitting in Iso communication. However, a scheme in which such data are transmitted by using Async communication among audio-video (AV) apparatuses has not been conceived.
The present invention, which has been achieved in view of such problems, provides means for transmitting data having a small amount of data, such as the above-mentioned still data, in Async communication.
An apparatus of the present invention is an apparatus for use in a system which performs communications among a plurality of electronic apparatuses that are connected by a bus capable of performing Iso and Async communications, wherein the apparatus comprises a data descriptor into which data for an object of Async communication is written.
A data communication method of the present invention is a method which performs communications among a plurality of electronic apparatuses that are connected by a bus capable of performing Iso and Async communications, the data communication method comprising the steps of: writing data which can be selected from a data source inside an electronic apparatus on the transmission side into a data descriptor; and transmitting the data read from the data descriptor in Async communication.
A data communication method of the present invention is a method which performs communications among a plurality of electronic apparatuses that are connected by a bus capable of performing Iso and Async communications, the data communication method comprising the step of: transmitting in Async communication data of contents which can be selected from a data source inside an electronic apparatus on the transmission side into a data descriptor inside an electronic apparatus on the receiving side.
According to the present invention, the electronic apparatus on the transmission side writes data which can be selected from a data source inside the apparatus into a data descriptor, and transmits the data read from the data descriptor in Async communication.
According to the present invention, the electronic apparatus on the transmission side transmits data of contents which can be selected from a data source inside the apparatus on the transmission side in Async communication.
The above and further objects, aspects and novel features of the invention will become more apparent from the following detailed description when read in connection with the accompanying drawings.